The influence of the submerged plants Ceratophyllum demersum L. and Elodea canadensis Michx. and the floating plant Hydrocharis morsus ranae L. on the species composition and quantitative parameters of a zooplankton community was studied experimentally. Among submerged vegetation, the development of the predaceous calanid Heterocope saliens Lilljeborg was suppressed. An increase in the number of zooplank ter species was observed in all experimental ecosystems with hydrophytes. The species similarity of zooplank ton was higher between communities with plants of the same ecological group than with plants of different groups. The highest average zooplankton biomass, as determined by the abundance of Daphnia longispina O.F. Müller and Simocephalus vetulus (O.F. Müller), was observed in experiments with Elodea. The highest average abundance over the experimental period was recorded among Ceratophyllum, where the abundance of Rotifera, chydorids, and copepods common in hydrophyte beds was higher than in other versions of the experiment.

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The aim of the work was to investigate the effect of cyanobacteria and elodea on population characteristics (abundance, biomass, fecundity) and “health” indicators (embryo status, heart rate and thermal resistance) of aquatic invertebrates in microcosms with controlled conditions. In July-August 2018, four treatments with environmental conditions of the coastal zone of the Rybinsk Reservoir during the period of cyanobacterial bloom were modeled. Mass species of plankton (with 80% dominance of large Daphnia longispina) and benthic animals (Unio pictorum, Gmelinoides fasciatus, Asellus aquaticus) and Elodea canadensis were placed in microcosms. In treatments with cyanobacteria, the toxic microcystins-LR were detected (24-53% of the sum of toxins, or 6,6-66,5 µg/l). The cyanobacteria Aphanizomenon flos-aquae, Microcystis aeruginosa and Gloeoitrichia spp. affected the structure of plankton reflecting in a decrease in the amount of green algae and an increase in the abundance of small crustaceans. Under the influence of cyanobacteria, variables of benthic animals differed significantly from control treatment, including a reduced level of thermal resistance of mollusks and amphipods, an increased recovery time of the heart rate after loading (salinity test) in mollusks, a decrease in individual fecundity, and an increase in the frequency of malformations and embryo mortality in amphipods. The presence of elodea enhanced these effects. Thus, the mass development of cyanobacteria and elodea affects the physiological status of sensitive species of aquatic animals, reducing their adaptability to natural stresses and worsening the quality of offspring.

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